Within a manufacturing line, it is sometimes necessary to have a limited number of production units over a given time go through particular designated areas of the manufacturing line, for instance to be tested and/or analyzed. Often a list of sequential process steps is specified for each production unit to denote each step that must be completed before the unit may proceed to the next step.
A testing and/or analysis operation is often a time-consuming operation, therefore it is desirable to sample only a limited number of production units on which to perform such tests, using sampling techniques designed to assure the sample group is representative of the pool of all production units. Precisely because the results of testing or analysis so performed on the sample group is considered to be representative of the pool from which the sample was taken, every unit in the pool is a candidate for selection into the sample group, even though the majority of these production units are not ultimately selected to be in the sample group that is actually tested and/or analyzed.
In a production line where only a limited number of units are selected for inspection, and where this selection requires diverting a selected unit from the normal flow of the production line to a designated station, there is need for a selection process which does not impede the normal flow of the production line. Such process, and the system implementing the process, must select representative units for testing without creating a back up of units during the selection process. In the past, all units waited in the queue for the designated station, while this selection was made randomly and manually by multiple workers using frequency logs to track the number or units tested or analyzed per weekly period. Typically, the manufacturing line backed up awaiting this determination, resulting in increased manufacturing time for all production units.
Systems and methods for scheduling or controlling work through manufacturing processes and/or collecting manufacturing data and applying it to process controllers are known.
U.S. Pat. No. 4,691,830, issued to Ahl et al. and assigned to Owens-Illinois, Inc., describes a completely automated system for inspection and sorting of molded containers, such as glass bottles, in a manufacturing process. The system in Ahl et al. is restricted to molded container manufacture, but is capable of distinguishing differing container cavity designs, automatically sampling a single container from each design for inspection at a predetermined time interval, comparing the inspection results with predetermined data and determining if a re-sample is required, automatically diverting all containers of a newly encountered cavity design for inspection until a predetermined number is reached, and automatically resetting upon a predetermined time corresponding to the factory worker shift change.
What is missing from the prior art, however, is a sampling process and associated system implementing a process that prevents production backups at the point of sampling while at the same time assuring representative sampling by selecting production units on the basis of a number of a combination of criteria, such as predetermined time intervals, response to the total number of units produced, and a periodic quota.